No Change to NAAQS for Ozone, Particulate Matter

US EPA will retain, without change, the current National Ambient Air Quality Standards (NAAQS) for both ozone and particulate matter.

EPA announced its final decision to retain the primary and secondary NAAQS for particulate matter on December 18.

The final decision to retain the NAAQS for ozone was announced on December 23. The decision was proposed in August 2020.

What Are NAAQS?

National Ambient Air Quality Standards (NAAQS) are protective limits on the volume of six “criteria pollutants” in the air we breath. The six criteria pollutants are nitrogen oxide, sulfur dioxide, carbon monoxide, lead, ozone, and particulate matter (PM).  

The Clean Air Act requires EPA to review the NAAQS for each of the six criteria pollutants once every five years and, if necessary, adjust them. In areas where pollution levels rise above the NAAQS (i.e., “non-attainment areas”), facilities face more stringent requirements for building or modifying sources of air pollution.

Read more: Quick Guide to National Air Quality Standards

What is Ozone?

Ground-level (“tropospheric”) ozone is harmful to human health and the environment. A primary factor in the creation of smog, ozone forms when nitrogen oxides and volatile organic compounds (VOCs) react with heat and sunlight.  

Breathing ozone can harm lung tissue and exacerbate respiratory maladies like bronchitis, emphysema, and asthma. Ozone can kill plants, as well, by negatively impacting photosynthesis and increasing plants' sensitivity to disease, insect damage, and severe weather.

EPA lowered the NAAQS for ozone to 70 parts per billion (ppb) in 2015.

What is Particulate Matter?

Particulate matter (PM) is generic term used to describe a class of particles that can originate from both man-made sources (e.g., coal-fired power plants) and natural sources (e.g., forest fires).

These particles vary in size and EPA categorizes them as follows:

• Course particulates (PM10) are particulates 10 microns or smaller
• Fine particulates (PM2.5) are particulates 2.5 microns or smaller  

Short- and long-term exposure to particulate matter contributes to decreased lung function and other adverse health effects in humans.  

EPA’s Back-to-Basics Approach to NAAQS Reviews

In 2018, EPA released a memo that listed five “back to basics” principles for NAAQS reviews. Number one on the list was to meet statutory deadlines, something EPA has struggled with historically.

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Tags: Clean Air Act, NAAQS, new rules